I am trying to create a basic HTML game using the Canvas element, but I am having trouble with it. Unfortunately, I don't know where the error is in my code, so I have posted the entirety of the document I'm working on below.
My problem: The canvas is not displaying when I run the HTML document.
This code's based off of (as in it pretty much is) the Movement tutorial from w3schools for using the Canvas, available at https://www.w3schools.com/graphics/tryit.asp?filename=trygame_movement_keyboard, but when chaing variable names I must've broken something, because after looking at this for hours I can't figure out what I'm missing.
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
border:1px solid #d3d3d3;
background-color: #f1f1f1;
}
</style>
</head>
<body onload = "initial()">
<script>
var playerOne;
function initial() {
playerOne = new canvasObject(30, 30, "red", 225, 225);
gameArea.start();
}
var gameArea = {
canvas : document.createElement("canvas");
start : function() {
this.canvas.width = 480;
this.canvas.height = 270;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateGameArea, 20);
window.addEventListener('keydown', function (e) {
e.preventDefault();
gameArea.keys = (gameArea.keys || []);
gameArea.keys[e.keyCode] = (e.type == "keydown");
})
window.addEventListener('keyup', function (e) {
gameArea.keys[e.keyCode] = (e.type == "keydown");
})
},
stop : function() {
clearInterval(this.interval);
},
clear : function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function canvasObject(width, height, color, x, y, type)
{
this.type = type;
this.width = width;
this.height = height;
this.speed = 0;
this.angle = 0;
this.moveAngle = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = gameArea.context;
ctx.save();
ctx.translate(this.x, this.y);
ctx.rotate(this.angle);
ctx.fillStyle = color;
ctx.fillRect(this.width / -2, this.height / -2, this.width, this.height);
ctx.restore();
}
this.newPos = function() {
this.angle += this.moveAngle * Math.PI / 180;
this.x += this.speed * Math.sin(this.angle);
this.y -= this.speed * Math.cos(this.angle);
}
}
function updateGameArea() {
gameArea.clear();
playerOne.moveAngle = 0;
playerOne.speed = 0;
if (gameArea.keys && gameArea.keys[37]) {
playerOne.moveAngle = -1;
}
if (gameArea.keys && gameArea.keys[39]) {
playerOne.moveAngle = 1;
}
if (gameArea.keys && gameArea.keys[38]) {
playerOne.speed= 1;
}
if (gameArea.keys && gameArea.keys[40]) {
playerOne.speed= -1;
}
playerOne.newPos();
playerOne.update();
}
</script>
</body>
</html>
gameArea is an object. Object properties are separated with ,, not ;. Hence, there is a syntax error after the definition of canvas.
var playerOne;
function initial() {
playerOne = new canvasObject(30, 30, "red", 225, 225);
gameArea.start();
}
var gameArea = {
canvas : document.createElement("canvas"),
start : function() {
this.canvas.width = 480;
this.canvas.height = 270;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateGameArea, 20);
window.addEventListener('keydown', function (e) {
e.preventDefault();
gameArea.keys = (gameArea.keys || []);
gameArea.keys[e.keyCode] = (e.type == "keydown");
})
window.addEventListener('keyup', function (e) {
gameArea.keys[e.keyCode] = (e.type == "keydown");
})
},
stop : function() {
clearInterval(this.interval);
},
clear : function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function canvasObject(width, height, color, x, y, type)
{
this.type = type;
this.width = width;
this.height = height;
this.speed = 0;
this.angle = 0;
this.moveAngle = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = gameArea.context;
ctx.save();
ctx.translate(this.x, this.y);
ctx.rotate(this.angle);
ctx.fillStyle = color;
ctx.fillRect(this.width / -2, this.height / -2, this.width, this.height);
ctx.restore();
}
this.newPos = function() {
this.angle += this.moveAngle * Math.PI / 180;
this.x += this.speed * Math.sin(this.angle);
this.y -= this.speed * Math.cos(this.angle);
}
}
function updateGameArea() {
gameArea.clear();
playerOne.moveAngle = 0;
playerOne.speed = 0;
if (gameArea.keys && gameArea.keys[37]) {
playerOne.moveAngle = -1;
}
if (gameArea.keys && gameArea.keys[39]) {
playerOne.moveAngle = 1;
}
if (gameArea.keys && gameArea.keys[38]) {
playerOne.speed= 1;
}
if (gameArea.keys && gameArea.keys[40]) {
playerOne.speed= -1;
}
playerOne.newPos();
playerOne.update();
}
canvas {
border:1px solid #d3d3d3;
background-color: #f1f1f1;
}
<body onload = "initial()">
You have a syntax error:
var gameArea = {
canvas : document.createElement("canvas");
...
}
You've used ; instead of ,
Related
When the component or square touches the bottom of the canvas and I press the up arrow afterwards it collides with the bottom, every jump the component jumps when I press the up arrow it jumps upwards less and less until the component eventually does not jump at all. But the component at the same time moves left and right perfectly still when this problem occurs.
I am controlling the square with the arrow keys and it is the player for this platform game that i am creating and i have no clue how i can change it.
var myGamePiece;
var platformWidth = 500;
var platformX = 0;
var platformY = 250;
function startGame() {
myGameArea.start();
myGamePiece = new component(30, 30, "red", 10, 120);
}
var myGameArea = {
canvas: document.createElement("canvas"),
start: function() {
this.canvas.width = 480;
this.canvas.height = 270;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.interval = setInterval(updateGameArea, 20);
window.addEventListener("keydown", function(e) {
myGameArea.key = e.keyCode;
});
window.addEventListener("keyup", function(e) {
myGameArea.key = false;
});
},
clear: function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
};
function component(width, height, color, x, y, type) {
this.type = type;
this.width = width;
this.height = height;
this.x = x;
this.y = y;
this.speedX = 0;
this.speedY = 0;
this.gravity = 0.05;
this.gravitySpeed = 0;
this.update = function() {
ctx = myGameArea.context;
ctx.fillStyle = color;
ctx.fillRect(this.x, this.y, this.width, this.height);
};
this.newPos = function() {
this.gravitySpeed += this.gravity;
this.x += this.speedX;
this.y += this.speedY + this.gravitySpeed;
this.hitBottom();
};
this.hitBottom = function() {
var rockbottom = myGameArea.canvas.height - this.height;
if (this.y > rockbottom) {
this.y = rockbottom;
if (myGameArea.canvas.height - this.height && myGamePiece.key == 38) {
this.y = this.speedY;
}
}
};
}
function updateGameArea() {
myGameArea.clear();
myGamePiece.speedX = 0;
myGamePiece.speedY = 0;
if (myGameArea.key && myGameArea.key == 37) {
myGamePiece.speedX = -5;
}
if (myGameArea.key && myGameArea.key == 39) {
myGamePiece.speedX = 5;
}
if (myGameArea.key && myGameArea.key == 38) {
myGamePiece.speedY = -5;
} else {
myGamePiece.speedY = 5;
}
if (myGameArea.key && myGameArea.key == 40) {
myGamePiece.speedY = 5;
}
myGamePiece.newPos();
myGamePiece.update();
}
startGame();
Did you forget to reset the gravity speed?
this.hitBottom = function() {
// ...
if (this.y > rockbottom) {
// ...
this.gravitySpeed = 0; // reset?
}
};
var myGamePiece;
var platformWidth = 360;
var platformX = 0;
var platformY = 120;
function startGame() {
myGameArea.start();
myGamePiece = new Component(12, 12, "red", 10, 10);
}
var myGameArea = {
canvas: document.createElement("canvas"),
start: function() {
this.canvas.width = platformWidth;
this.canvas.height = platformY;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.interval = setInterval(updateGameArea, 20);
window.addEventListener("keydown", function(e) {
myGameArea.key = e.keyCode;
});
window.addEventListener("keyup", function(e) {
myGameArea.key = false;
});
},
fill: function(color) {
this.context.save();
this.context.fillStyle = color;
this.context.fillRect(0, 0, this.canvas.width, this.canvas.height);
this.context.restore();
},
clear: function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
};
function Component(width, height, color, x, y, type) {
this.type = type;
this.width = width;
this.height = height;
this.x = x;
this.y = y;
this.speedX = 0;
this.speedY = 0;
this.gravity = 0.05;
this.gravitySpeed = 0;
this.update = function() {
ctx = myGameArea.context;
ctx.fillStyle = color;
ctx.fillRect(this.x, this.y, this.width, this.height);
};
this.newPos = function() {
this.gravitySpeed += this.gravity;
this.x += this.speedX;
this.y += this.speedY + this.gravitySpeed;
this.hitBottom();
};
this.hitBottom = function() {
var rockbottom = myGameArea.canvas.height - this.height;
if (this.y > rockbottom) {
this.y = rockbottom;
if (myGameArea.canvas.height - this.height && myGamePiece.key == 38) {
this.y = this.speedY;
}
this.gravitySpeed = 0; // reset?
}
};
}
function updateGameArea() {
myGameArea.fill('#DE7');
myGamePiece.speedX = 0;
myGamePiece.speedY = 0;
if (myGameArea.key) {
switch (myGameArea.key) {
case 37: // left arrow
myGamePiece.speedX = -5;
break;
case 38: // up arrow
myGamePiece.speedY = -5;
break;
case 39: // right arrow
myGamePiece.speedX = +5;
break;
case 40: // down arrow
default:
myGamePiece.speedY = +5;
}
}
myGamePiece.newPos();
myGamePiece.update();
}
startGame();
body {
background: #000;
}
Here is another approach using classes, you can clean up the vector math, by using actual vector classes e.g. Victor.js.
const main = () => {
new GravityGame({
width : 360,
height : 180,
refreshRate : 20
}).start();
}
class AbstractGameClient {
constructor(options) {
this.refreshRate = options.refreshRate
this.view = new GameArea({
width : options.width,
height : options.height
})
}
update() {
this.view.update()
}
start() {
let self = this
self.intervalId = setInterval(function() { self.update() }, self.refreshRate)
return self
}
stop() {
if (self.intervalId) {
clearInterval(self.intervalId)
}
}
}
class GravityGame extends AbstractGameClient {
constructor(options) {
super(options)
let myGamePiece = new Component({
width : 12,
height : 12,
color : 'red'
})
this.view.addComponent(myGamePiece)
}
}
class GameArea {
constructor(options) {
let self = this
self.canvas = document.createElement('canvas')
self.width = options.width
self.height = options.height
self.key = null
self.components = []
self.addListeners()
self.render()
}
render() {
let self = this
self.canvas.width = self.width
self.canvas.height = self.height
self.context = self.canvas.getContext('2d')
document.body.insertBefore(self.canvas, document.body.childNodes[0])
}
addComponent(component) {
this.centerComponent(component)
this.components.push(component)
}
addListeners() {
let self = this;
window.addEventListener('keydown', function(e) {
self.key = e.keyCode;
});
window.addEventListener('keyup', function(e) {
self.key = false;
});
}
fill(color) {
this.context.save();
this.context.fillStyle = color;
this.context.fillRect(0, 0, this.canvas.width, this.canvas.height);
this.context.restore();
}
clear() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
update() {
let self = this
let speed = { x : 0, y : 0 }
if (self.key) {
switch (self.key) {
case 37: // left arrow
speed.x = -5;
break;
case 38: // up arrow
speed.y = -5;
break;
case 39: // right arrow
speed.x = +5;
break;
case 40: // down arrow
default:
speed.y = +5;
}
}
self.fill('#DE7')
self.components.forEach(component => {
component.speed.x = speed.x
component.speed.y = speed.y
component.reposition(self.context)
component.redraw(self.context)
})
}
centerComponent(component) {
let xOffset = Math.floor((this.canvas.width / 2) - component.width / 2)
let yOffset = Math.floor((this.canvas.height / 2) - component.height / 2)
component.position = { x : xOffset, y : yOffset }
}
};
class Component {
constructor(options) {
let self = this
self.width = options.width
self.height = options.height
self.position = options.position
self.color = options.color
self.type = options.type
self.speed = { x : 0, y : 0 }
self.gravity = { x : 0, y : 0.05 };
self.acceleration = { x : 0, y : 0 };
}
redraw(context) {
context.fillStyle = this.color;
context.fillRect(this.position.x, this.position.y, this.width, this.height);
}
reposition(context) {
let self = this
// Increase acceleration
self.acceleration.x += self.gravity.x;
self.acceleration.y += self.gravity.y;
// pos + speed + acceleration
self.position.x += self.speed.x + self.acceleration.x;
self.position.y += self.speed.y + self.acceleration.y;
self.checkBounds(context);
}
checkBounds(context) {
let self = this
let rockbottom = context.canvas.height - this.height
if (self.position.y > rockbottom) {
self.position.y = rockbottom
if (context.canvas.height - self.height && self.key == 38) {
self.position.y = self.speed.y
}
self.acceleration = { x : 0, y : 0 } // reset
}
}
}
main();
body {
background: #000;
}
var car;
var front;
var back;
var carpoint1;
var carpoint2;
var carpoint3;
var carpoint4;
var img = new Image();
img.src = 'https://cdn4.iconfinder.com/data/icons/transportation-2-4/60/transportation-2-flat-036-racing-car-top-512.png';
function startGame() {
car = new move(12, 20, "red", 600, 300);
pg.start();
}
var pg = {
canvas : document.createElement("canvas"),
start : function() {
this.canvas.width = 1200;
this.canvas.height = 600;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateframe, 20);
window.addEventListener('keydown', function (e) {
e.preventDefault();
pg.keys = (pg.keys || []);
pg.keys[e.keyCode] = (e.type == "keydown");
})
window.addEventListener('keyup', function (e) {
pg.keys[e.keyCode] = (e.type == "keydown");
})
},
stop : function() {
clearInterval(this.interval);
},
clear : function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function move(width, height, color, x, y, type) {
this.type = type;
this.width = width;
this.height = height;
this.speed = 0;
this.angle = 0;
this.moveAngle = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = pg.context;
ctx.save();
getcarpoints(this.x, this.y, this.angle);
ctx.translate(this.x, this.y);
ctx.rotate(this.angle);
ctx.drawImage(img, this.width / -2, this.height / -2,20,40);
ctx.restore();
ctx.beginPath();
ctx.moveTo(300, 150);
ctx.lineTo(600, 800);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(300, 150);
ctx.lineTo(carpoint1[0], carpoint1[1]);
ctx.stroke();
}
this.newPos = function() {
this.angle += this.moveAngle * Math.PI / 180;
this.x += this.speed * Math.sin(this.angle);
this.y -= this.speed * Math.cos(this.angle);
}
}
function getcarpoints(prex,prey,rotation)
{
carpoint1=[getrotatedx(prex,prey,rotation), getrotatedy(prex,prey,rotation)];
carpoint2=[carpoint1[0], carpoint1[1]+40];
carpoint3=[carpoint2[0]+20, carpoint2[1]+40];
carpoint4=[carpoint3[0]+20, carpoint3[1]];
// console.log(carpoint1[0]);
}
function getrotatedx(prex,prey,rotation)
{
piangle=Math.abs((rotation/ Math.PI * 180)%360);
newx=Math.cos(piangle)*prex+(-(Math.sin(piangle)*prey));
return newx;
}
function getrotatedy(prex,prey,rotation)
{
piangle=Math.abs((rotation/ Math.PI * 180)%360);
newy=Math.sin(piangle)*prex+(Math.cos(piangle)*prey);
return newy;
}
function updateframe() {
pg.clear();
car.moveAngle = 0;
car.speed = 0;
if (pg.keys && pg.keys[37]) { if (pg.keys && pg.keys[40]) {car.moveAngle= 5; } if (pg.keys && pg.keys[38]){car.moveAngle = -5; } }
if (pg.keys && pg.keys[39]) { if (pg.keys && pg.keys[40]) {car.moveAngle= -5; } if (pg.keys && pg.keys[38]){car.moveAngle = 5; } }
if (pg.keys && pg.keys[38]) {car.speed= 5; }
if (pg.keys && pg.keys[40]) {car.speed= -5; }
car.newPos();
car.update();
}
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
border:1px solid #d3d3d3;
background-color: #f1f1f1;
}
</style>
</head>
<body onload="startGame()">
<script src="control.js"></script>
</body>
</html>
Here is my full code in snippet. I am trying to make a line from one fix point to the car... and this is the problem.
Now when is horizontal at any x point it works perfectly but the moment car turn the angle changes and it all messes up! you can see that when you turn the car (use arrow and left or right arrow at the same time) the line jumps.
Note: it is my project requirement to do it with 2d rotation matrix which means I can't make the line before i restore the canvas.
carpoint1,2,3,4 are the corners of car but right now I am just working with the carpoint1.
Do something so getrotatedx and getrotatedy always gives correct value that are car coordinates after matrix rotation.
Use ctx.lineTo(this.x, this.y); instead of ctx.lineTo(carpoint1[0], carpoint1[1]);
var car;
var front;
var back;
var carpoint1;
var carpoint2;
var carpoint3;
var carpoint4;
var img = new Image();
img.src = 'https://cdn4.iconfinder.com/data/icons/transportation-2-4/60/transportation-2-flat-036-racing-car-top-512.png';
function startGame() {
car = new move(12, 20, "red", 600, 300);
pg.start();
}
var pg = {
canvas : document.createElement("canvas"),
start : function() {
this.canvas.width = 1200;
this.canvas.height = 600;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateframe, 20);
window.addEventListener('keydown', function (e) {
e.preventDefault();
pg.keys = (pg.keys || []);
pg.keys[e.keyCode] = (e.type == "keydown");
})
window.addEventListener('keyup', function (e) {
pg.keys[e.keyCode] = (e.type == "keydown");
})
},
stop : function() {
clearInterval(this.interval);
},
clear : function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function move(width, height, color, x, y, type) {
this.type = type;
this.width = width;
this.height = height;
this.speed = 0;
this.angle = 0;
this.moveAngle = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = pg.context;
ctx.save();
getcarpoints(this.x, this.y, this.angle);
ctx.translate(this.x, this.y);
ctx.rotate(this.angle);
ctx.drawImage(img, this.width / -2, this.height / -2,20,40);
ctx.restore();
ctx.beginPath();
ctx.moveTo(300, 150);//fixed point
ctx.lineTo(600, 800);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(300, 150);
ctx.lineTo(this.x, this.y);
ctx.stroke();
}
this.newPos = function() {
this.angle += this.moveAngle * Math.PI / 180;
this.x += this.speed * Math.sin(this.angle);
this.y -= this.speed * Math.cos(this.angle);
}
}
function getcarpoints(prex,prey,rotation)
{
carpoint1=[getrotatedx(prex,prey,rotation), getrotatedy(prex,prey,rotation)];
carpoint2=[carpoint1[0], carpoint1[1]+40];
carpoint3=[carpoint2[0]+20, carpoint2[1]+40];
carpoint4=[carpoint3[0]+20, carpoint3[1]];
// console.log(carpoint1[0]);
}
function getrotatedx(prex,prey,rotation)
{
piangle=Math.abs((rotation/ Math.PI * 180)%360);
newx=Math.cos(piangle)*prex+(-(Math.sin(piangle)*prey));
return newx;
}
function getrotatedy(prex,prey,rotation)
{
piangle=Math.abs((rotation/ Math.PI * 180)%360);
newy=Math.sin(piangle)*prex+(Math.cos(piangle)*prey);
return newy;
}
function updateframe() {
pg.clear();
car.moveAngle = 0;
car.speed = 0;
if (pg.keys && pg.keys[37]) { if (pg.keys && pg.keys[40]) {car.moveAngle= 5; } if (pg.keys && pg.keys[38]){car.moveAngle = -5; } }
if (pg.keys && pg.keys[39]) { if (pg.keys && pg.keys[40]) {car.moveAngle= -5; } if (pg.keys && pg.keys[38]){car.moveAngle = 5; } }
if (pg.keys && pg.keys[38]) {car.speed= 5; }
if (pg.keys && pg.keys[40]) {car.speed= -5; }
car.newPos();
car.update();
}
startGame()
canvas {
border:1px solid #d3d3d3;
background-color: #f1f1f1;
}
var car;
var front;
var back;
var img = new Image();
img.src = 'https://cdn4.iconfinder.com/data/icons/transportation-2-4/60/transportation-2-flat-036-racing-car-top-512.png';
function startGame() {
car = new move(12, 20, "red", 600, 300);
pg.start();
}
var pg = {
canvas: document.createElement("canvas"),
start: function() {
this.canvas.width = 1200;
this.canvas.height = 600;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateframe, 20);
window.addEventListener('keydown', function(e) {
e.preventDefault();
pg.keys = (pg.keys || []);
pg.keys[e.keyCode] = (e.type == "keydown");
})
window.addEventListener('keyup', function(e) {
pg.keys[e.keyCode] = (e.type == "keydown");
})
},
stop: function() {
clearInterval(this.interval);
},
clear: function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function move(width, height, color, x, y, type) {
this.type = type;
this.width = width;
this.height = height;
this.speed = 0;
this.angle = 0;
this.moveAngle = 0;
this.x = x;
this.y = y;
this.update = function() {
ctx = pg.context;
ctx.save();
ctx.translate(this.x, this.y);
ctx.rotate(this.angle);
ctx.drawImage(img, this.width / -2, this.height / -2,20,40);
ctx.beginPath();
ctx.moveTo(this.width / -2, this.height / -2);
ctx.lineTo(this.width / -2, 30);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(this.width / -2, 30);
ctx.lineTo(13, (this.height / -2)+40);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(14, (this.height / -2)+40);
ctx.lineTo(14, this.height / -2);
ctx.stroke();
ctx.beginPath();
ctx.moveTo(14, this.height / -2);
ctx.lineTo(this.width / -2, this.height / -2);
ctx.stroke();
ctx.restore();
ctx.beginPath();
ctx.moveTo(300, 150);
ctx.lineTo(600, 800);
ctx.stroke();
}
this.newPos = function() {
this.angle += this.moveAngle * Math.PI / 180;
this.x += this.speed * Math.sin(this.angle);
this.y -= this.speed * Math.cos(this.angle);
}
}
function updateframe() {
pg.clear();
car.moveAngle = 0;
car.speed = 0;
if (pg.keys && pg.keys[37]) {
if (pg.keys && pg.keys[40]) {
car.moveAngle = 5;
}
if (pg.keys && pg.keys[38]) {
car.moveAngle = -5;
}
}
if (pg.keys && pg.keys[39]) {
if (pg.keys && pg.keys[40]) {
car.moveAngle = -5;
}
if (pg.keys && pg.keys[38]) {
car.moveAngle = 5;
}
}
if (pg.keys && pg.keys[38]) {
car.speed = 5;
}
if (pg.keys && pg.keys[40]) {
car.speed = -5;
}
car.newPos();
car.update();
}
startGame();
canvas {
border: 1px solid #d3d3d3;
background-color: #f1f1f1;
}
There is a car and a line, now i want to make an alert whenever the car get touched by the the line.
I know how to do this logically. like if i convert the car image in four lines (border) then use line intersection formula to get if there is a intersection but i am new to this canvas drawing and i cant figure how to get the border line equation of car.
update: i have made lines of border around the car, now i just need help with getting if these lines intersects with each other...
code is updated plz check it now...
one more thing, at this point there is only one line and i am going to add more lines in it... so i need a function to call it more often and get if the lines are intersecting with car border...
Note : use arrow keys to move car in snippet
I can't figure out how I can make myGamePiece jump using the up-key. First I tried the simple "myGamePiece.speedY = 1", but this doesn't work. Nor does trying to reverse "this.gravitySpeed" in the function. Can someone help me and if possible explain why mine don't work and yours does? Thanks in advance! My excuses if it seems to long, I'm unable to shorten it even further without removing the code of the component.
A litle explaination for the code:
function startGame: Starts the game
var myGameArea: Allows to multiply press two keys
function component: generates the object and its characteristics
function updateGameArea: Allows for the movement of the object
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
border:1px solid #d3d3d3;
background-color: #f1f1f1;
}
</style>
</head>
<body onload="startGame()">
<script>
var myGamePiece;
function startGame() {
myGamePiece = new component(30, 30, "red", 80, 75);
myGameArea.start();
}
var myGameArea = {
canvas : document.createElement("canvas"),
start : function() {
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.interval = setInterval(updateGameArea, 20);
window.addEventListener('keydown', function (e) {
myGameArea.keys = (myGameArea.keys || []);
myGameArea.keys[e.keyCode] = true;
})
window.addEventListener('keyup', function (e) {
myGameArea.keys[e.keyCode] = false;
})
},
clear : function() {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function component(width, height, color, x, y, type) {
this.width = width;
this.height = height;
this.x = x;
this.y = y;
this.gravity = 0.05;
this.gravitySpeed = 0;
this.update = function() {
ctx = myGameArea.context;
ctx.fillStyle = color;
ctx.fillRect(this.x, this.y, this.width, this.height);
}
this.newPos = function() {
this.gravitySpeed += this.gravity;
this.x += this.speedX;
this.y += this.speedY + this.gravitySpeed;
this.hitBottom();
}
this.hitBottom = function() {
var rockbottom = myGameArea.canvas.height - this.height;
if (this.y > rockbottom) {
this.y = rockbottom;
}
}
}
function updateGameArea() {
myGameArea.clear();
myGamePiece.speedX = 0;
myGamePiece.speedY = 0;
if (myGameArea.keys && myGameArea.keys[37]) {myGamePiece.speedX = -2; }
if (myGameArea.keys && myGameArea.keys[39]) {myGamePiece.speedX = 2; }
if (myGameArea.keys && myGameArea.keys[38]) {myGamePiece.speedY = -1; }
if (myGameArea.keys && myGameArea.keys[40]) {myGamePiece.speedY = 1; }
myGamePiece.newPos();
myGamePiece.update();
}
</script>
</body>
</html>
The problem is that the value of the gravitySpeed variable is constantly increasing.
Try to reset the gravitySpeed variable value to 0 in your hitBottom check:
if (this.y > rockbottom) {
this.y = rockbottom;
this.gravitySpeed = 0;
}
You may also want to view values of some parameters in real time while you debugging:
add a block like this to your html
<div style="position:absolute; width: 300px; bottom: 50px; right: 50px;">
<p>sppedY: <span id="speedY"></span></p>
<p>gravitySpeed: <span id="gravitySpeed"></span></p>
<p>posY: <span id="posY"></span></p>
</div>
and a block like this in your updateGameArea function
...
myGamePiece.newPos();
// -- debug --
speedY.innerText = myGamePiece.speedY.toFixed(2);
gravitySpeed.innerText = myGamePiece.gravitySpeed.toFixed(2);
posY.innerText = myGamePiece.y.toFixed(2);
// -----------
myGamePiece.update();
I have taken an image and made it into my gamepiece put on a canvas, but I cannot get it to rotate properly. I apologize if my code is not very organized just got a little bit hurried. The problem will lie in the component function. Thank you for your help!
var myGamePiece;
function startGame() {
myGamePiece = new component(40, 40, "character.png", 300, 300, "image");
myGameArea.start();
}
var myGameArea = {
canvas: document.createElement("canvas")
, start: function () {
this.canvas.width = 640;
this.canvas.height = 480;
this.context = this.canvas.getContext("2d");
document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateGameArea, 20);
window.addEventListener('keydown', function (e) {
e.preventDefault();
myGameArea.keys = (myGameArea.keys || []);
myGameArea.keys[e.keyCode] = (e.type == "keydown");
})
window.addEventListener('keyup', function (e) {
myGameArea.keys[e.keyCode] = (e.type == "keydown");
})
}
, stop: function () {
clearInterval(this.interval);
}
, clear: function () {
this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
}
}
function component(width, height, color, x, y, type) {
this.type = type;
if (type == "image") {
this.image = new Image();
this.image.src = color;
}
this.width = width;
this.height = height;
this.speed = 0;
this.angle = 0;
this.moveAngle = 0;
this.x = x;
this.y = y;
this.update = function () {
ctx = myGameArea.context;
if (type == "image") {
ctx.save();
ctx.rotate(this.angle);
ctx.drawImage(this.image, this.x, this.y, this.width, this.height);
ctx.restore();
} else {
ctx.save();
ctx.translate(this.x, this.y);
ctx.fillStyle = color;
ctx.fillRect(this.width / -2, this.height / -2, this.width, this.height);
}
}
this.newPos = function () {
this.angle += this.moveAngle * Math.PI / 180;
this.x += this.speed * Math.sin(this.angle);
this.y -= this.speed * Math.cos(this.angle);
}
this.hitBottom = function () {
var bottom = myGameArea.canvas.height - 20;
if (this.y > bottom) {
this.y = this.y - 2.5;
}
}
this.hitTop = function () {
if (this.y < 20) {
this.y = this.y + 2.5;
}
}
this.hitLeft = function () {
if (this.x < 20) {
this.x = this.x + 2.5;
}
}
this.hitRight = function () {
var side = myGameArea.canvas.width - 20;
if (this.x > side) {
this.x = this.x - 2.5;
}
}
}
function updateGameArea() {
myGameArea.clear();
myGamePiece.moveAngle = 0;
myGamePiece.speed = 0;
if (myGameArea.keys && myGameArea.keys[37]) {
myGamePiece.moveAngle = -2.5;
}
if (myGameArea.keys && myGameArea.keys[39]) {
myGamePiece.moveAngle = 2.5;
}
if (myGameArea.keys && myGameArea.keys[38]) {
myGamePiece.speed = 2.5;
}
if (myGameArea.keys && myGameArea.keys[40]) {
myGamePiece.speed = -1;
}
myGamePiece.newPos();
myGamePiece.update();
myGamePiece.hitBottom();
myGamePiece.hitTop();
myGamePiece.hitLeft();
myGamePiece.hitRight();
}